The present invention relates to a method of driving an ink jet recording head used for a recording apparatus, such as a printer and a plotter, and more particularly to an ink jet recording head capable of plural kinds of ink drops of different volumes through the same nozzle orifice.
In the ink jet recording head used for the printing device, a called "pull and shoot" control method is used in which a pressure generating chamber is expanded, and then is contracted to eject an ink drop through a nozzle orifice. In this control method controls an expansion of the pressure generating chamber to thereby control the volume of an ink drop to be ejected.
To eject a relatively large ink drop, the pressure generating chamber is controlled so that the meniscus (free surface) of ink in the nozzle orifice stays at a position near the front edge of the nozzle orifice, and then the pressure generating chamber is contracted. As a result, a large amount of ink is ejected through the nozzle orifice, to form an ink drop for forming a large dot.
To eject a relatively small ink drop, the pressure generating chamber is expanded so as to pull the meniscus toward the pressure generating chamber, and in this state, the pressure generating chamber is contracted. In this case, an ink drop of a small volume is ejected through the nozzle orifice. That is, the ink drop is for forming a small dot.
To perform a gradation print by use of ink drops of different volumes, small and large dots are printed on the same line on a recording medium or paper.
To print a pattern containing small dots X1 and large dots X2 as shown in FIG. 11(a), in a first scan (first path), the recording head is moved in the main scanning direction to print the small dots X1 (FIG. 11(b)). In a second scan (second path), the recording head is moved in the main scanning direction to print the large dots X2 (FIG. 11(c)).
Thus, a plurality of printing operations are repeated along one printing line. This is because a driving signal (driving pulse) for large dots and another driving signal for small dots are separately generated. The large-dot driving signal and the small-dot driving signal are separately generated, and those signals are selectively applied to the recording head every printing operation (printing path). Therefore, a plurality of the printing operations is repeated along one printing line inevitably.
As described above, the small dots Xl and the large dots X2 are printed on the same printing line. This results in reduction of the printing speed.
There is possibility that the scanning speeds for the printing operations of the small dots X1 and the large dots X2 lose their uniformity. If the scanning speeds lose their uniformity, the landing positions of the ink drops, viz., the landing center positions of the small and large dots X1 and X2, are deviated from the correct positions every size (diameter) of ink drop. The result is degradation of the print quality.